There is known a hybrid vehicle that includes a power split mechanism which is connected with an internal combustion engine, a motor generator, and an output portion, and that is capable of splitting power of the internal combustion engine into the output portion and the motor generator by the power split mechanism. In such a vehicle, there is known a vehicle that is provided with an engagement mechanism which is capable of switching between an engagement state where an output shaft of the motor generator is locked so as not to rotate and a release state where the output shaft locked is released, and that a variable gear ratio mode and a fixed gear ratio mode are realized by switching a state of the engagement mechanism (see Patent Literature 1). In addition, there are Patent Literatures 2-5 as prior art references in relation to the present invention.